package sntp;

import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * This class represents a NTP message, as specified in RFC 2030. The message
 * format is compatible with all versions of NTP and SNTP.
 *
 * This class does not support the optional authentication protocol, and
 * ignores the key ID and message digest fields.
 * <p>
 * For convenience, this class exposes message values as native Java types, not
 * the NTP-specified data formats. For example, timestamps are
 * stored as doubles (as opposed to the NTP unsigned 64-bit fixed point
 * format).
 * <p>
 * However, the contructor NtpMessage(byte[]) and the method toByteArray()
 * allow the import and export of the raw NTP message format.
 * <p>
 * <p>
 * Usage example
 * <p>
 * // Send message
 * DatagramSocket socket = new DatagramSocket();
 * InetAddress address = InetAddress.getByName("ntp.cais.rnp.br");
 * byte[] buf = new NtpMessage().toByteArray();
 * DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 123);
 * socket.send(packet);
 * <p>
 * // Get response
 * socket.receive(packet);
 * System.out.println(msg.toString());
 * <p>
 * <p>
 * This code is copyright (c) Adam Buckley 2004
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version. A HTML version of the GNU General Public License can be
 * seen at http://www.gnu.org/licenses/gpl.html
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 * <p>
 * <p>
 * Comments for member variables are taken from RFC2030 by David Mills,
 * University of Delaware.
 * <p>
 * Number format conversion code in NtpMessage(byte[] array) and toByteArray()
 * inspired by http://www.pps.jussieu.fr/~jch/enseignement/reseaux/
 * NTPMessage.java which is copyright (c) 2003 by Juliusz Chroboczek
 * <p>
 * @author Adam Buckley
 */
public class NtpMessage
{
	/**
	 * This is a two-bit code warning of an impending leap second to be
	 * inserted/deleted in the last minute of the current day. It's values
	 * may be as follows:
	 * <p>
	 * Value Meaning
	 * ----- -------
	 * 0 no warning
	 * 1 last minute has 61 seconds
	 * 2 last minute has 59 seconds)
	 * 3 alarm condition (clock not synchronized)
	 */
	public byte leapIndicator = 0;

	/**
	 * This value indicates the NTP/SNTP version number. The version number
	 * is 3 for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI).
	 * If necessary to distinguish between IPv4, IPv6 and OSI, the
	 * encapsulating context must be inspected.
	 */
	public byte version = 3;

	/**
	 * This value indicates the mode, with values defined as follows:
	 * <p>
	 * Mode Meaning
	 * ---- -------
	 * 0 reserved
	 * 1 symmetric active
	 * 2 symmetric passive
	 * 3 client
	 * 4 server
	 * 5 broadcast
	 * 6 reserved for NTP control message
	 * 7 reserved for private use
	 * <p>
	 * In unicast and anycast modes, the client sets this field to 3 (client)
	 * in the request and the server sets it to 4 (server) in the reply. In
	 * multicast mode, the server sets this field to 5 (broadcast).
	 */
	public byte mode = 0;

	/**
	 * This value indicates the stratum level of the local clock, with values
	 * defined as follows:
	 * <p>
	 * Stratum Meaning
	 * ----------------------------------------------
	 * 0 unspecified or unavailable
	 * 1 primary reference (e.g., radio clock)
	 * 2-15 secondary reference (via NTP or SNTP)
	 * 16-255 reserved
	 */
	public short stratum = 0;

	/**
	 * This value indicates the maximum interval between successive messages,
	 * in seconds to the nearest power of two. The values that can appear in
	 * this field presently range from 4 (16 s) to 14 (16284 s); however, most
	 * applications use only the sub-range 6 (64 s) to 10 (1024 s).
	 */
	public byte pollInterval = 0;

	/**
	 * This value indicates the precision of the local clock, in seconds to
	 * the nearest power of two. The values that normally appear in this field
	 * range from -6 for mains-frequency clocks to -20 for microsecond clocks
	 * found in some workstations.
	 */
	public byte precision = 0;

	/**
	 * This value indicates the total roundtrip delay to the primary reference
	 * source, in seconds. Note that this variable can take on both positive
	 * and negative values, depending on the relative time and frequency
	 * offsets. The values that normally appear in this field range from
	 * negative values of a few milliseconds to positive values of several
	 * hundred milliseconds.
	 */
	public double rootDelay = 0;

	/**
	 * This value indicates the nominal error relative to the primary reference
	 * source, in seconds. The values that normally appear in this field
	 * range from 0 to several hundred milliseconds.
	 */
	public double rootDispersion = 0;

	/**
	 * This is a 4-byte array identifying the particular reference source.
	 * In the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
	 * stratum-1 (primary) servers, this is a four-character ASCII string, left
	 * justified and zero padded to 32 bits. In NTP Version 3 secondary
	 * servers, this is the 32-bit IPv4 address of the reference source. In NTP
	 * Version 4 secondary servers, this is the low order 32 bits of the latest
	 * transmit timestamp of the reference source. NTP primary (stratum 1)
	 * servers should set this field to a code identifying the external
	 * reference source according to the following list. If the external
	 * reference is one of those listed, the associated code should be used.
	 * Codes for sources not listed can be contrived as appropriate.
	 * <p>
	 * Code External Reference Source
	 * ---- -------------------------
	 * LOCL uncalibrated local clock used as a primary reference for
	 * a subnet without external means of synchronization
	 * PPS atomic clock or other pulse-per-second source
	 * individually calibrated to national standards
	 * ACTS NIST dialup modem service
	 * USNO USNO modem service
	 * PTB PTB (Germany) modem service
	 * TDF Allouis (France) Radio 164 kHz
	 * DCF Mainflingen (Germany) Radio 77.5 kHz
	 * MSF Rugby (UK) Radio 60 kHz
	 * WWV Ft. Collins (US) Radio 2.5, 5, 10, 15, 20 MHz
	 * WWVB Boulder (US) Radio 60 kHz
	 * WWVH Kaui Hawaii (US) Radio 2.5, 5, 10, 15 MHz
	 * CHU Ottawa (Canada) Radio 3330, 7335, 14670 kHz
	 * LORC LORAN-C radionavigation system
	 * OMEG OMEGA radionavigation system
	 * GPS Global Positioning Service
	 * GOES Geostationary Orbit Environment Satellite
	 */
	public byte[] referenceIdentifier =
	{
		0, 0, 0, 0
	};

	/**
	 * This is the time at which the local clock was last set or corrected, in
	 * seconds since 00:00 1-Jan-1900.
	 */
	public double referenceTimestamp = 0;

	/**
	 * This is the time at which the request departed the client for the
	 * server, in seconds since 00:00 1-Jan-1900.
	 */
	public double originateTimestamp = 0;

	/**
	 * This is the time at which the request arrived at the server, in seconds
	 * since 00:00 1-Jan-1900.
	 */
	public double receiveTimestamp = 0;

	/**
	 * This is the time at which the reply departed the server for the client,
	 * in seconds since 00:00 1-Jan-1900.
	 */
	public double transmitTimestamp = 0;

	/**
	 * Constructs a new NtpMessage from an array of bytes.
	 */
	public NtpMessage( byte[] array )
	{
		// See the packet format diagram in RFC 2030 for details
		leapIndicator = ( byte ) ((array[0] >> 6) & 0x3);
		version = ( byte ) ((array[0] >> 3) & 0x7);
		mode = ( byte ) (array[0] & 0x7);
		stratum = unsignedByteToShort(array[1]);
		pollInterval = array[2];
		precision = array[3];

		rootDelay = (array[4] * 256.0)
						+ unsignedByteToShort(array[5])
						+ (unsignedByteToShort(array[6]) / 256.0)
						+ (unsignedByteToShort(array[7]) / 65536.0);

		rootDispersion = (unsignedByteToShort(array[8]) * 256.0)
						+ unsignedByteToShort(array[9])
						+ (unsignedByteToShort(array[10]) / 256.0)
						+ (unsignedByteToShort(array[11]) / 65536.0);

		referenceIdentifier[0] = array[12];
		referenceIdentifier[1] = array[13];
		referenceIdentifier[2] = array[14];
		referenceIdentifier[3] = array[15];

		referenceTimestamp = decodeTimestamp(array, 16);
		originateTimestamp = decodeTimestamp(array, 24);
		receiveTimestamp = decodeTimestamp(array, 32);
		transmitTimestamp = decodeTimestamp(array, 40);
	}

	/**
	 * Constructs a new NtpMessage in client -> server mode, and sets the
	 * transmit timestamp to the current time.
	 */
	public NtpMessage()
	{
		// Note that all the other member variables are already set with
		// appropriate default values.
		this.mode = 3;
		this.transmitTimestamp = (org.joda.time.DateTimeUtils.currentTimeMillis() / 1000.0) + 2208988800.0;
	}

	/**
	 * This method constructs the data bytes of a raw NTP packet.
	 */
	public byte[] toByteArray()
	{
		// All bytes are automatically set to 0
		byte[] p = new byte[48];

		p[0] = ( byte ) (leapIndicator << 6 | version << 3 | mode);
		p[1] = ( byte ) stratum;
		p[2] = ( byte ) pollInterval;
		p[3] = ( byte ) precision;

		// root delay is a signed 16.16-bit FP, in Java an int is 32-bits
		int l = ( int ) (rootDelay * 65536.0);
		p[4] = ( byte ) ((l >> 24) & 0xFF);
		p[5] = ( byte ) ((l >> 16) & 0xFF);
		p[6] = ( byte ) ((l >> 8) & 0xFF);
		p[7] = ( byte ) (l & 0xFF);

		// root dispersion is an unsigned 16.16-bit FP, in Java there are no
		// unsigned primitive types, so we use a long which is 64-bits
		long ul = ( long ) (rootDispersion * 65536.0);
		p[8] = ( byte ) ((ul >> 24) & 0xFF);
		p[9] = ( byte ) ((ul >> 16) & 0xFF);
		p[10] = ( byte ) ((ul >> 8) & 0xFF);
		p[11] = ( byte ) (ul & 0xFF);

		p[12] = referenceIdentifier[0];
		p[13] = referenceIdentifier[1];
		p[14] = referenceIdentifier[2];
		p[15] = referenceIdentifier[3];

		encodeTimestamp(p, 16, referenceTimestamp);
		encodeTimestamp(p, 24, originateTimestamp);
		encodeTimestamp(p, 32, receiveTimestamp);
		encodeTimestamp(p, 40, transmitTimestamp);

		return p;
	}

	/**
	 * Returns a string representation of a NtpMessage
	 */
	public String toString()
	{
		String precisionStr
						= new DecimalFormat("0.#E0").format(Math.pow(2, precision));

		return "Leap indicator: " + leapIndicator + "\n"
						+ "Version: " + version + "\n"
						+ "Mode: " + mode + "\n"
						+ "Stratum: " + stratum + "\n"
						+ "Poll: " + pollInterval + "\n"
						+ "Precision: " + precision + " (" + precisionStr + " seconds)\n"
						+ "Root delay: " + new DecimalFormat("0.00").format(rootDelay * 1000) + " ms\n"
						+ "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion * 1000) + " ms\n"
						+ "Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + "\n"
						+ "Reference timestamp: " + timestampToString(referenceTimestamp) + "\n"
						+ "Originate timestamp: " + timestampToString(originateTimestamp) + "\n"
						+ "Receive timestamp:   " + timestampToString(receiveTimestamp) + "\n"
						+ "Transmit timestamp:  " + timestampToString(transmitTimestamp);
	}

	/**
	 * Converts an unsigned byte to a short. By default, Java assumes that
	 * a byte is signed.
	 */
	public static short unsignedByteToShort( byte b )
	{
		if ( (b & 0x80) == 0x80 )
		{
			return ( short ) (128 + (b & 0x7f));
		}
		else
		{
			return ( short ) b;
		}
	}

	/**
	 * Will read 8 bytes of a message beginning at <code>pointer</code>
	 * and return it as a double, according to the NTP 64-bit timestamp
	 * format.
	 */
	public static double decodeTimestamp( byte[] array, int pointer )
	{
		double r = 0.0;

		for ( int i = 0; i < 8; i++ )
		{
			r += unsignedByteToShort(array[pointer + i]) * Math.pow(2, (3 - i) * 8);
		}

		return r;
	}

	/**
	 * Encodes a timestamp in the specified position in the message
	 */
	public static void encodeTimestamp( byte[] array, int pointer, double timestamp )
	{
		// Converts a double into a 64-bit fixed point
		for ( int i = 0; i < 8; i++ )
		{
			// 2^24, 2^16, 2^8, .. 2^-32
			double base = Math.pow(2, (3 - i) * 8);

			// Capture byte value
			array[pointer + i] = ( byte ) (timestamp / base);

			// Subtract captured value from remaining total
			timestamp = timestamp - ( double ) (unsignedByteToShort(array[pointer + i]) * base);
		}

		// From RFC 2030: It is advisable to fill the non-significant
		// low order bits of the timestamp with a random, unbiased
		// bitstring, both to avoid systematic roundoff errors and as
		// a means of loop detection and replay detection.
		array[7] = ( byte ) (Math.random() * 255.0);
	}

	/**
	 * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
	 * formatted date/time string.
	 */
	public static String timestampToString( double timestamp )
	{
		if ( timestamp == 0 )
		{
			return "0";
		}

		// timestamp is relative to 1900, utc is used by Java and is relative
		// to 1970
		double utc = timestamp - (2208988800.0);

		// milliseconds
		long ms = ( long ) (utc * 1000.0);

		// date/time
		String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms));

		// fraction
		double fraction = timestamp - (( long ) timestamp);
		String fractionSting = new DecimalFormat(".000000").format(fraction);

		return date + fractionSting;
	}

	/**
	 * Returns a string representation of a reference identifier according
	 * to the rules set out in RFC 2030.
	 */
	public static String referenceIdentifierToString( byte[] ref, short stratum, byte version )
	{
		// From the RFC 2030:
		// In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
		// or stratum-1 (primary) servers, this is a four-character ASCII
		// string, left justified and zero padded to 32 bits.
		if ( stratum == 0 || stratum == 1 )
		{
			return new String(ref);
		}

		// In NTP Version 3 secondary servers, this is the 32-bit IPv4
		// address of the reference source.
		else
		{
			if ( version == 3 )
			{
				return unsignedByteToShort(ref[0]) + "."
								+ unsignedByteToShort(ref[1]) + "."
								+ unsignedByteToShort(ref[2]) + "."
								+ unsignedByteToShort(ref[3]);
			}

			// In NTP Version 4 secondary servers, this is the low order 32 bits
			// of the latest transmit timestamp of the reference source.
			else
			{
				if ( version == 4 )
				{
					return "" + ((unsignedByteToShort(ref[0]) / 256.0)
									+ (unsignedByteToShort(ref[1]) / 65536.0)
									+ (unsignedByteToShort(ref[2]) / 16777216.0)
									+ (unsignedByteToShort(ref[3]) / 4294967296.0));
				}
			}
		}

		return "";
	}
}
